Ditto on the wide-angle...it comes in so much more handy than you even think of. As someone who frequents the parks very often each year, I took photos for years with advanced P&S models that were usually around 36mm equivelent at the widest. Though I had great fun and took tens of thousands of photos, only the purchase of a DSLR and access to a wider lens has made me realize how many photos I couldn't take before. With an 18mm wide end (1.5x sensor crop = 27mm), I can now shoot entire building facades, whereas before I could back up right to the wall or fence and still couldn't squeeze the buildings in.
If you can afford it, I heartily recommend an all-purpose wide to tele zoom. The convenience of not having to change lenses for virtually any photographic situation is hard to beat. I predominantly use an 18-250mm zoom, which gives me wide angle to super-tele in one small package, and I can shoot wildlife at AK to wide scenes at HS, action shots to night shots...all with one lens.
I still bring other lenses along, and use them on occasion in the parks - my 50mm F1.7 gets used for low light photography and ride photography sometimes - but generally the 18-250 is the perfect Disney lens, and gets used 98% of the time.
Now go have fun!!
